Java中高效判断数组中是否包含某个元素的几种方法

public static boolean useList(String[] arr, String targetValue) {

     return Arrays.asList(arr).contains(targetValue);

}

public static boolean useSet(String[] arr, String targetValue) {

     Set<String> set = new HashSet<String>(Arrays.asList(arr));

     return set.contains(targetValue);

}

public static boolean useLoop(String[] arr, String targetValue) {

     for (String s: arr){

         if (s.equals(targetValue))

             return true ;

     }

     return false ;

}

public static boolean useArraysBinarySearch(String[] arr, String targetValue) {

     int a =  Arrays.binarySearch(arr, targetValue);

     if (a > 0 )

         return true ;

     else

         return false ;

}

public static void main(String[] args) {

     String[] arr = new String[] {  "CD" ,  "BC" , "EF" , "DE" , "AB" };

     //use list

     long startTime = System.nanoTime();

     for ( int i = 0 ; i < 100000 ; i++) {

         useList(arr, "A" );

     }

     long endTime = System.nanoTime();

     long duration = endTime - startTime;

     System.out.println( "useList:  " + duration / 1000000 );

     //use set

     startTime = System.nanoTime();

     for ( int i = 0 ; i < 100000 ; i++) {

         useSet(arr, "A" );

     }

     endTime = System.nanoTime();

     duration = endTime - startTime;

     System.out.println( "useSet:  " + duration / 1000000 );

     //use loop

     startTime = System.nanoTime();

     for ( int i = 0 ; i < 100000 ; i++) {

         useLoop(arr, "A" );

     }

     endTime = System.nanoTime();

     duration = endTime - startTime;

     System.out.println( "useLoop:  " + duration / 1000000 );

     //use Arrays.binarySearch()

     startTime = System.nanoTime();

     for ( int i = 0 ; i < 100000 ; i++) {

         useArraysBinarySearch(arr, "A" );

     }

     endTime = System.nanoTime();

     duration = endTime - startTime;

     System.out.println( "useArrayBinary:  " + duration / 1000000 );

}

String[] arr = new String[ 1000 ];

Random s = new Random();

for ( int i= 0 ; i< 1000 ; i++){

     arr[i] = String.valueOf(s.nextInt());

}

String[] arr = new String[ 10000 ];

Random s = new Random();

for ( int i= 0 ; i< 10000 ; i++){

     arr[i] = String.valueOf(s.nextInt());

}

import org.apache测试数据mons.lang3.ArrayUtils;

public static boolean useArrayUtils(String[] arr, String targetValue) {

     return ArrayUtils.contains(arr,targetValue);

}

if (array == null ) {

        return - 1 ;

    } else {

        if (startIndex < 0 ) {

            startIndex = 0 ;

        }

        int i;

        if (objectToFind == null ) {

            for (i = startIndex; i < array.length; ++i) {

                if (array[i] == null ) {

                    return i;

                }

            }

        } else if (array.getClass().getComponentType().isInstance(objectToFind)) {

            for (i = startIndex; i < array.length; ++i) {

                if (objectToFind.equals(array[i])) {

                    return i;

                }

            }

        }

        return - 1 ;

    }

package zaLearnpackage;

import org.apache测试数据mons.lang3.ArrayUtils;

import java.util.Arrays;

import java.util.HashSet;

import java.util.Set;

//检查数组是否包含某个值的方法

public class TestArray {

     //使用List

public static boolean useList(String[] arr,String targetValue){

     return Arrays.asList(arr).contains(targetValue);

}

//使用Set

public static boolean useSet(String[] arr,String targetValue){

     Set<String> set= new HashSet<String>(Arrays.asList(arr));

     return set.contains(targetValue);

}

//使用循环判断

public static boolean useLoop(String[] arr,String targetValue){

     for (String s:arr){

         if (s.equals(targetValue))

             return true ;

         } 

         return false ;

     }

//查找有序数组中是否包含某个值的用法

public static boolean useArraysBinarySearch(String[] arr,String targetValue){

     int a=Arrays.binarySearch(arr, targetValue);

     if (a> 0 )

         return true ;

     else

         return false ;

}

//使用ArrayUtils

public static boolean useArrayUtils(String[] arr,String targetValue){

     return ArrayUtils.contains(arr,targetValue);

}

public static void main(String[] args) {

     String[] arr= new String[]{ "CD" , "BC" , "EF" , "DE" , "AB" , "JK" };

     //use list

     long startTime=System.nanoTime();

     for ( int i= 0 ;i< 100000 ;i++){

         useList(arr, "A" );

     }

     long endTime=System.nanoTime();

     long duration=endTime-startTime;

     System.out.println( "useList:" +duration/ 1000000 );

     //use set

         long startTime2=System.nanoTime();

         for ( int i= 0 ;i< 100000 ;i++){

             useSet(arr, "A" );

         }

         long endTime2=System.nanoTime();

         long duration2=endTime2-startTime2;

         System.out.println( "useSet:" +duration/ 1000000 );

         //use loop

         long startTime3=System.nanoTime();

         for ( int i= 0 ;i< 100000 ;i++){

             useLoop(arr, "A" );

         }

         long endTime3=System.nanoTime();

         long duration3=endTime3-startTime3;

         System.out.println( "useLoop:" +duration/ 1000000 );

         //use Arrays.binarySearch()

         long startTime4=System.nanoTime();

         for ( int i= 0 ;i< 100000 ;i++){

             useArraysBinarySearch(arr, "A" );

         }

         long endTime4=System.nanoTime();

         long duration4=endTime4-startTime4;

         System.out.println( "useArraysBinarySearch:" +duration/ 1000000 );

}

}

/*

  * 显然，使用一个简单的循环方法比使用任何集合都更加高效。许多开发人员为了方便，都使用第一种方法，但是他的效率也相对较低。因为将数组压入Collection类型中，首先要将数组元素遍历一遍，然后再使用集合类做其他操作。

  */

String inputStrs = "北京,天津,上海,四川,湖南,广州,深圳,海南" ;

String[] strList = inputStrs.split( "," );

String target = "上海" ; //1

String result = Arrays.asList(strList).contains(target) ? "查到咯！" : "没这个城市啊..." ;

//2Set<String> set = new HashSet<>(Arrays.asList(strList));

System.out.println(set.contains(target)); // true

System.out.println(result); // result="查到咯！"-----------